Refining pig iron



Dec. 5, 1967 F. MULLER r-:TAL 3,356,490

REFINING PIG IRON Filed April 23, 1965 I 5 Sheets-Sheet 1 Dec. 5, 1967F. MULLER ETAI.

REFINING PIG IRON 5 Sheets-Sheet 2 Filed April 25, 1965 Dec. 5, 1967 F.-MULLER ETAL REFINING PIG IRON 5 Sheets-Sheet 5 Filed April 25, 1965 Dec.5, 1967 F. MULLER ETAL REFINING PIG IRON 5 Sheets-Sheet 4 Filed April25, 1965 Dec. 5, 1967 F, MULLER ETAL 3,356,490

REFINING PIG IRON Filed April 25, 1965 5 Sheets-Sheet 5 c in megg Mn inmetal Fe In sluq l' l' l l I (I \f Y //z J? l. Y' 4 J if me ""utesDuration of overlow ofslaq United States Patent 6 claims. (ci. *7s-6a)The present invention relates to improvements in processes for refiningpig iron. Recently introduced techniques, which have now become wellknown, for refining pig iron comprise the top blowing of a bath ofliquid pig iron with an oxidizing gas which may or may not containslag-forming materials in suspension. Such processes have been used tomake steels of a quality fully comparable with open hearth steels andelectric steels while often reducing costs substantially. In the case ofphosphorus-containing pig iron these known processes usually comprisetwo blowing periods at least, separated by a slagging operation. Such aslagging operation however has certain disadvantages such as loss oftime, loss of heat, and an increase in the wear of the refractories ofthe vessel holding the metal since the metal remains in it longer.

On the other hand haematitic pig ironl can be refined in a single phase,that is to say without an intermediate slagging operation, though it hasnot been found economically advantageous to use the same slag from thebeginning to the very end of the refining operation since the slag doesnot remain sufficiently fluid and reactive till the end of the processsince it contains too many impurities.

One particular object of the present invention is the provision of aprocess which enables the majority of the above-mentioned disadvantagesto be overcome While providing several advantages as well.

ln the process in accordance with the invention a haematitic orphosphorus-containing pig iron is blown with an oxidizing gas, such ascommercially pure oxygen, and the blowing is carried out in such amanner as to produce a foaming slag, at least part of this foaming slagbeing evacuated from the refining vessel as it is formed. The evacuationcan take place during all or during only part of the operation. Theoxidizing gas can contain in suspension slag-forming materials.

It has been found that one advantage of the process in accordance withthe invention is that a fresh and reactive slag is continually formedowing to the supply of slagforming materials in the gas. Owing to thecontinuous evacuation of foaming slag which has already reacted at leastpartially with the metal, the physical and chemical reactions of therefining process are accelerated and the equilibrium points aredisplaced so as to obtain a purer metal.

The vessel used for carrying out the invention can have a low volume,for instance between 0.3 and 0.7 cubic meter per metric ton of pig iron.The volume is therefore comparatively low since in conventionalapparatus it is usually between 0.7 cubic meter and 1.4 cubic meters permetric ton of pig iron. This is evidently a substantial ad- Vantage ofthe invention.

The evacuation of the foaming slag can take place either by allowing itto overflow over its rim or through a lateral opening in the vesselplaced ata carefully chosen height.

The choice of the height should be made to ensure that the volume ofslag is small enough to enable a rapid change-over in the slag to takeplace without the lateral opening being so low that granules of metalare lost to any great extent with the slag being evacuated. It has beenfound that the height of the slag divided by the height of the bathshould be between 0.5 and 1.5. In practice of course it can be adjustedby tipping the vessel.

If the degree of foaming is insufficient several methods can be used forincreasing it; for instance by adding materials such as oxides of iron,chromium oxide, graphite, and magnesia to the slag, either by themselvesor as constituents of powders containing slag-forming materials blowninto the bath with a lance. These slag-forming materials can be addedcontinuously throughout a refining operation or heat so as to make surethat the slag is always capable of taking up impurities from the metalbeing refined. It has been found that graphite and magnesia have theadvantage over iron oxides of decreasing the quantity of iron lost inthe slag being continually removed. Although the materials for provokingfoaming can be in powder form they can also be in the particle sizerange 2 mm. to 100 mm. and this has been found specially so in the caseof graphite.

Though it is difficult to lay down a general rule for the quantity offoam-provoking agents to be added for all steels and all grades ofcast-iron, it is considered that they should make up between l and 10%of the slag in the vessel.

A second method of causing continuous foaming of the slag consists inmaintaining the lower end of the lance used for refining below thelowest part of the opening for the removal of slag and controllingfoaming of ythe slag using known techniques of blowing, i.e. to producean emulsion. This technique has the advantage of facilitating deeppenetration of the jet of oxidizing gas into the metal and thusaccelerating reactions between the metal and the slag. The method isparticularly advantageous when fresh slag-forming and foam-provokingmaterials are added continuously so that the level of the foaming slagis sufficiently high to cause continuous operation.

A further method of provoking foaming of the slag consists in using alance whose bore diameter in mm. is not less than 0.02 times thediameter of the bath in meters divided by the square root of theabsolute pressure-of the refining gas in atmospheres.

The yield of the process can be increased by placing the refining lanceeccentrically in relation to the axis of the vessel between the axis andthe lateral opening for the removal of slag, and it has been found thatthis arrangement substantially reduces throwing of particles or granulesof metal towards the slag-removal opening. Therefore there is less riskof the particles of metal being drawn out of the vessel in the slag bythe refining jet through the lateral opening. Such a loss of -metal canalso be reduced by directing preferably oblique jets of gals towards thetop of the vessel so as to sweep back granules of metal from theslag-removal opening and thus favour the contact of the metal and theslag.

The removal of slag at the beginning of the operation is facilitated byusing a slag-removal opening which is comparatively small, andpressurizing the inside of the vessel so that gas and fumes producedduring the refining are obliged to pass out through the slag-removalopening and thus help the removal of foaming slag.

The times at which slag should be removed and the rate at which it isremoved should be related to the chemical composition of the slag, forinstance having regard to its iron oxide and P205 contents. It istherefore advantageous to refrain :from removing slag unless the slagcontains a certain maximum quantity of iron oxide (for instance 20%) andla certain minimum quantity of P205.

The composition of slag should be chosen so that there is no likelihoodof two immiscible slag phases arising.

The content of iron oxide should be kept low so as to prevent such anoccurrence, as can be seen from an examination of a ternary diagram ofP2O5-CaO-Fe0+ MnO At this moment, the quantity of iron carried out withthe slag in the course of slag removal can be considered as economicallyacceptable.

The continuously removed slag removed after this moment is richer inlime and P205 than the slag formed initially at the beginning of arefining operation and is therefore more suitable for agricultural uses.The content of iron oxide, low when slag is first removed, decreases toa minimum and then increases again. The continuous removal of slagshould therefore be stopped so as to keep the losses of iron oxidewithin reasonable limits.

The ternary diagram represented in FIGURE l of the accompanying drawing,in which I and II indicate respectively the zone of immiscibility andthe zone of lime saturation, indicates by way of example the manner inwhich this form of invention may be carried out. The variations inchemical composition during the course of an operation are shownschematically so as to indicate the limiting compositions of the slag.Thus in the curve showing the variations of composition the parts ab andcd represent the variation in composition when slag is not beingcontinually removed, while the part bc represents the variation of thecomposition when the slag is continuously removed.

In order to provide for easy control of the quantity of slag removed andto estimate its iron content at any given instant, the slag ispreferably weighed continuously and the rate of slag formation ismodified as desired, for instance by tilting the vessel so that theratio between the depths of the slag and of the metal is changed.

It is known that at a certain point, the iron oxide content of the slagbegins to increase in such a fashion that the slag has a composition atthe end of the ope-ration which enables a low phosphorus content to beattained in the metallic bath. At this moment it is necessary to slowdown or even stop the flow of the slag from the vessel for the purposeof avoiding a reduction in the yield of refined metal.

By means of analysing the composition of the slag it is possible todetermine the moment at which it is convenient to reduce or stop theremoval of the slag; however continuous Weighing is quicker and simpler.Another advantage of continuous Weighing (preferably carried out withelectronic weighing equipment), results from the fact that if thecontent of metallic iron in the slag increases suddenly, the suddenincrease in the weight of the slag is quickly detected so that theoperator can react rapidly to take effective steps to limit losses iniron, something that would not be possible with other methods. Suchother methods being based on computations of the total quantities oflime and oxygen injected bear less relation to the composition of theslag.

It has been found that the quantity of citric acid soluble P205, whichis important from the agricultural point of view, is more particularlyrelated to the percentage of silica divided by the percentage of P205 inthe slag and, to achieve solubility, this ratio should always be above0.3.

In accordance with the invention it has been found comparatively easy toproduce a slag having a P205 content sufficient to give a high citricacid solubility. Thus, to achieve this, during the whole of the refiningoperation blowing is carried out in such a manner with the addition ofslag-forming materials, for instance limestone, that the liquid slagemerging from the vessel or converter always contains at least 14%, andpreferably 18% of P205 and as the refining operation proceeds silicaorsiliconcon taining materials yare added so that the silica-P205 ratioalways exceeds 0.3.

These additions can, in accordance with this embodiment of theinvention, be carried out preferably outside the refining vessel.

lDifferent processes can be used for slowing down or stopping theproduction or the removal of slag. One can for example change the heightof the blowing lance and/ or the rate of feed of lime or of oxygen.These methods though efficient are slow, and it has been found surer andmore effective to raise the height of the slag-removal opening bytilting the vessel. The slag-removal opening can be provided with anelongated lip. The slag level can be raised by using a block ofrefractory material, wood, or a plastic substance fitting in the openingso as to dam it.

The present invention has a further embodiment providing for therecovery of metal entrained with the slag as it is evacuated and forthis the slag is collected in a receptacle distinct from the refiningvessel. The slag can be separated from the metal in it by decantation orcentrifuging and the metal thus recovered can either be treated as beingfully refined or can be replaced in the vessel in the following heat.

In the case of decantation, the slag flowing from the vessel whenoverfiowing begins is preferably collected in an empty ladle which is inthe turned up position. Droplets of steel and metal are then separatedby decantation. The slag retained in the ladle during the decantationmay frequently have a relatively high silica content, since it willcontain a proportion of the slag that first overows from the refiningvessel and therefore the slag collected in the ladle, after steps havebeen taken to see that it is homogeneous, is particularly suitable foruse as an agricultural fertiliser. In the course of another phase ofoverflow, the ladle can be inclined in such a fashion that onlyparticles of metal are retained in it and the slag fiows continuously sothat the ladle only represents a temporary receptacle for the slagoverflowing from the refining vessel (for instance a converter) into afurther slag container. Towards the end of a heat, the ladle can betilted into its upright position again so as to retain the iron-richslag which then starts to flow, until the slag outlet opening is blockedor until the vessel is turned up. Proceeding thus, a mixing of thelastnamed, iron-rich slag, with the slag in the further slag containingvessel used, is avoided, something that would be unavoidable if theladle were not used during the blocking of the opening inthe converter.

It has been found that the particles of metal entrained with the slagare nearly or practically completely refined, and a further embodimentof the invention is based on an intentional encouragement of suchentrainment, the entrained metal being separated from the entrainingslag by decantation or centrifuging, while to make up for the loss ofmetal from the vessel, metal is continually added to it.

The partially or totally refined liquid metal can be forced out of therefining vessel by adding pig iron to the vessel either continuously orinterruptedly. The pig iron can be added from the side or from above,above or below the level of the bath through it is preferable to placeit in the bottom of the bath as directly as possible in order to avoiddisturbing the refining operation being carried out. Another reason foradding the pig iron to the bottom of the bath is that as the pig ironrises to the surface its temperature gradient increases anddecarburisation progresses.

The quantity of pig iron to be added is substantially equal to theamount of metal evacuated from the vessel. The rate at which pig iron isevacuated from the vessel can be controlled in various manners, forinstance by varying the distance between the lance and the bath orvarying the kinetic energy of the gas striking the bath. The gas can beprojected obliquely down on to the bath so as to vary its impactpressure and the quantity of slag-forming material suspended in the gascan be varied. Also it is possible to vary the pressure of the gas, theheight of the foaming slag and the pressure in the vessel.

If the metal evacuated from the vessel during the operation is notsufficiently refined, the treatment of the metal can be carried out in asecondary refining vessel in which the metal is subjected in acontinuous or discontinuous fashion to a reheating operation and then toa subsidiary refining operation in accordance with its conditionpossibly followed by the addition of alloying elements and todeoxidation.

A particularly advantageous form of process described in the lastpreceding paragraph consists in allowing the mixture of foaming slag andmetal falling from the primary vessel to drop into a secondary vessel(for example a ladle) provided with a means for separating the slag andthe metal, for example a tipping device for the carefully controlledpouring off of the supernatant slag, either continuously ordiscontinuously, from the secondary vessel while the metal remainsbehind in it.

The primary and secondary vessels or receptacles can be arranged in sucha manner that `while metal and foaming slag passes from the first vesselinto the second vessel, the metal is continually decanted from thesecond vessel.

On the other hand if a batch rather than a continuons method is used,the secondary vessel is allowed to fill with metal and a furthersecondary vessel is then filled from the primary vessel while the metalfrom the rst secondary vessel is given further treatment. This furthertreatment can be of a conventional nature though a preferred form of itcomprises injecting an oxidizing gas, preferably commercially pureoxygen, down intoA the metal and nely divided slag-forming materials maybe added in the gas. The metal after this treatment can be separatedfinally from its slag in a continuous or discontinuous manner, or, if itis needed, la further purifying treatment can be carried out. It istherefore possible to carry out a three-stage cascade continuous processof steel making in which the metal to be treated flows continuously fromthe primary vessel, then to the secondary vessel, and then to thetertiary vessel, pneumatic refining producing a foamingslag. beingcarried out in each vessel.

If such a continuous cascade process is used using two vessels insteadof threerthe operation can be carried `out in such a manner that alow-iron slag is used in the first vessel, for instance with an ironcontent between 5% and 30% and preferably between 10% and 20%, while theP205 content is at least This slag removed from the primary vessel istherefore of high value as a fertilizer for agriculture.

In the secondary vessel oxidation of the metal is encouraged so a-s toobtain an iron-rich slag which does not contain much phosphorus and canbe added to the primary vessel together with the necessary pig iron andscrap.

Scrap may be added to the secondary vessel. In order' t ously cast.

A further aspect of the invention is the pneumatic granulation of theslag produced since as the slag is produced continuously the granulatingapparatus can be considerably simpler than known apparatus in which theslag has to be stored while molten, since it is produced in batches,until it can be dealt with by the granulating device. 4

In accordance with the present invention the slag which is allowed torun continuously from the vessel in which steel is being produced isgranulated by means of one or more jets of gas or liquid blown obliquelyor perpendicularly towards the flow of liquid slag.

A further advantage of the present invention from the point of View ofgranulating slag pneumatically or by means of a liquid is that the slagsproduced are liquid and of fairly even consistency, as opposed to theslags produced in conventional batch processes for making steel. Thegranulation can be carried out on slag leaving any one of three stagesof a cascade process in accordance with the invention or on slag leavingall of them.

As for apparatus used for carrying out the invention,

the top blowing of a melt of pig iron so as to produce a foaming slagwhich is allowed to overfiow continuously can be carried out in anapproximately cylindrical vessel having a lateral opening and la solidfiat bottom. The top part of the vessel can converge conically.

The vessel can be provided with a cover to enable a gauge pressure to beobtained inside it so as to encourage fumes to emerge through thelateral opening together with some of the supernatant slag. The metalcan be teemed through a tapping hole in the side of the vesselpreferably opposite the lateral opening for the removal of slag. Thetapping hole is higher than the slag-removal opening, the verticalcomponent of the distance between both openings being preferably betweenone and two times the thickness of the slag, this being sufficient toprevent the slag emerging as it foams, without requiring anexceptionally tall vessel. As already mentioned the vessel can beprovided with an elongated lip or trough for guiding liquid slag leavingthrough the lateral opening. In order to discourage metal from fiowingout along such a trough, the bottom of the trough can be made so thatthe first part of it nearest the vessel slopes upwards or the troughcan-be provided with a separate interior duct which rotates.

Various embodiments of the invention and apparatus for carrying it outare now described with reference to the attached drawings.

FIGURE 1 (whic-h has already been described above) is a ternary diagramof the system P2O5-CaO-Fe0+ MnO FIGURES 2 and 3 show vessels in the formof converters for carrying out the process in accordance with theinvention.

FIGURE 4 is a section of a further converter.

FIGURE 5 shows yet another converter.

FIGURES 6 and 7 show methods of operating converters when carrying outthe process in accordance with the invention.

FIGURES 8 and 9 show an apparatus for carrying out the invention indifferent positions.

FIGURE 10 shows a further apparatus for carrying out the invention.

FIGURES l1 and 12 show somewhat similar apparatus.

FIGURE 13 illustrates a cascade steel-making process in acco-rdance withthe invention.

FIGURE 14 is a graph showing the course of a steelmaking operation inaccordance with invention.

As shown in the drawings, and with more particular reference to FIGURES2 and 3, it can be seen that the process of the invention in which pigiron is continuously top blown so as to produce a foaming slag on itwhich is allowed to overflow, can conveniently be carried out in anapproximately cylindrical converter vessel 1 provided with a lateralopening 2 for the continuous overflow of the slag, and a tapping opening3 for teeming the metal. The converter is provided with a cover 4 and alance 5 for the top blowing with an oxidizing gas such as commerciallypure oxygen containing slag-forming materials in suspension. The cover 4seals the top of the converter and causes the fumes generated in it tobe blown out through the lateral slag-removal opening 2 entraining withthem the foaming slag. For teeming the metal the vessel is turned downin a clockwise direction. FIGURE '3 shown asimilar apparatus forcarrying out the present invention.

centric position in relation to the center axis of the converter. Ittends to blow the foaming slag away from the slag outlet opening 2. Itwill be noted that the duct 2 leading from the slag outlet openingsslopes upwards to discourage the loss of metal from the vessel with theoverflowing slag.

In the converter shown in FIGURE 5 the process is v'carried out in sucha manner that the foaming slag overcylindrical so as to increase theslag capacity, to facilitate decantation of the steel, and reduce thequantity of metal entraiued with the slag leaving along the spout 8.Preferably the volume available for slag before it overflows and thatavailable for the metal should be in a ratio of between 0.25 and 3 orpreferably between 0.75 and 2.

The ratio in the actual embodiment shown is 1.96. In the converter shownin FIGURES 6 and 7 the overfiow `of slag can be reduced or shut offcompletely by tilting lin an anti-clockwise direction as shown in FIGURE7. 'The cover 4 of the converter is provided with a slot 4 which enablesthe converter to be tilted without moving the lance 5. The metal isrepresented by M. During refining slag is allowed to overflowcontinuously through 'the lateral opening 2. It will be noted that thislateral -opening is provided with a spout having a Weir 9 to hold .backthe metal.

The apparatus shown in FIGURE 8 comprises a converter vessel 1 similarto the converter vessel shown in FIGURE 5. Slag flows continuously fromit to a decanting `vessel 10 and thence into a slag container 11. Thedecanting vessel 10 can be in a horizontal position so as to retain `themetal and (temporarily) the slag or it can be inclined las shown inFIGURE 9 so that it only serves for decanting vthe metallic particles.The apparatus shown in FIGURE 9 is similar to that shown in FIGURE 8apart from the provision of a wall of the converter above the spout.

FIGURES 10, 11 and 12 all show apparatus for the continuous refining ofpig iron, that is to say apparatus in which the pig iron is caused toflow continually through :the apparatus instead of being treated inbatches.

In the apparatus shown in FIGURE 10 we utilise a Iconverter 1 fedcontinuously at its bottom with liquid pig iron through a duct 12. Thecover 4 is provided with an opening 4l whose size is chosen to achievethe desired pressure inside the vessel 1. Slag and metal fiow continu-Iously through the lateral opening 2 into a decanting vessel 13 provideswith decanting openings 14 and 15 for the removal of metal and slagrespectively. 16 indicates a device for the addition of ferro-manganese.

In the apparatus shown in FIGURE 11 scrap is added through a lateralopening 17 down a chute 18 and is preheated by fumes generated duringthe refining process.

yThe bore at the bottom of the lance 5 is inclined obliquely towards thelateral opening 2 for the removal of slag and metal. The decantingvessel 13 is similar to that shown in FIGURE 10 but cannot be tilted andhas a cover.

In the apparatus shown in FIGURE 12 the lance 5 is inclined and entersthe vessel through a side wall. An oxygen-hydrocarbon fuel burner 19serves for heating up the scrap as it enters the vessel.

As shown in FIGURE 13, apparatus for a cascade process for thecontinuous manufacture of steel from pig iron in accordance with theinvention comprises two vessels 1 in which the metal is refined by meansof top blowing with an oxidizing gas, for instance commercially pureoxygen, containing powdered lime in suspension. Metal and foaming slagcontinuously tiow from the primary vessel 1 into the decanting vessel 20which is provided with an overfiow 21 for the slag, which is low in ironand rich in phosphorus, and an outlet pipe 22 with an inverted U bend orsyphon for the removal of metal which flows into a second refiningvessel also denoted by the reference numeral 1 in which it is top blownagain by commercially pure oxygen containing lime in suspension. Theemulsion of slag and metal is allowed to overiiow into a furtherdecanting vessel 20 Where the slag which is rich in iron is removed andreturned to the first vessel 1. The steel passes from the vessel 20 to areceptacle 23 in which alloying elements and deoxidizing agents areadded. After leaving this receptacle the steel passes to a continuouscasting plant schematically indicated at 24.

For granulating the slag produced it is possible to provide jets ofliquid or gas acting on the slag as it ows continuously from the spoutof a ladle of slag, provision being made for tilting the ladles so thatthe rate of flow of slag can be maintained at an even rate.

The following is an example of a process embodying the invention.

An experimental converter was used having an internal diameter of cm.The converter was provided with a lateral opening with a diameter of 30cm., its bottom being 60 cm. above the level of the bath. The depth ofthe bath (composed of Thomas pig iron and cooling scrap) was 60 cm. Thebath contained two metric tons of metal with the following analysis:

Percent C 3.75 P 1.80 Si 0.3 Mn 0.2

Commercially pure oxygen was blown down on to the bath using a lancewhose -bore diameter was 21 mm. The rate of injection was 7.5 Nm.3 ofoxygen per minute. One minute after the beginning of the operation theinjection of lime powder was begun at the rate of 16 kg. per minute andthis was kept up for twelve minutes. Overflowing of the slag began atthe eighth minute and lasted for tive minutes. kg. of slag werecollected for each metric ton of metal.

The slag which overflowed had the following analysis:

Percent CaO 52 P205 21 Fe 15 SiO2 4 As the slag overfiowed the lance wasgradually lowered towards the bath. At the thirteenth minute the slagoverflow opening was blocked up with a refractory. The rate of feed oflime was then altered to 40 kg. per minute during a period of 11/2minutes while the feed of oxygen was reduced to 6 Nm.3 per minute untilthe end of the operation after nineteen minutes.

The graph of FIGURE 14 shows the changes in the composition of the metalas regards carbon, phosphorus, silicon and manganese and also as regardschanges in the iron content of the slag. The final content of the steel,as shown, was C, 0.04%, P, 0.015%, and S, 0.015%. The final slagcomposition was CaO, 50%, P205, 8%, SiO2, 3%, Fe, 25%.

The first slag was therefore quite suitable for use as a fertilizerwhile the second slag could be returned to the converter for use at thebeginning of a refining operation.

In a further embodiment of the invention the same converter was chargedwith 3 metric tons of pig iron and scrap and a decantation receptaclewas placed to receive material emerging from the lateral opening o-f theconverter. The slag was allowed to overflow out of this vessel into aslag container while metal was removed from a tapping hole in it andtransferred to a ladle in which final additions were made to achieve thedesired composition. A tilting ladle was placed somewhat above and tothe side of the converter so as to allow pig iron to flow continuouslyinto the converter. During the first part of the operation beforeoverflowing of metal began, the metal was top blown as described in thefirst example.

75 The slag that overflowed had the same composition as in the firstexample while the metal which was entrained with the slag into thedecantation receptacle had a carbon content of 0.05% and a phosphoruscontent of 0.015%.

While I have described specific embodiments of my invention so as toenable those skilled in the art to take full advantage of it, it is tobe understood that the monopoly I seek in the United States is not to belimited to these particular embodiments but is to be defined by the gistand spirit of the following patent claims.

We claim:

1. In a process of refining pig iron which comprises top blowing pigiron in a refining vessel with an oxidizing gas, the improvementcomprising producing a foaming slag on the molten metal, and removing atleast part of said foaming slag by continuously overflowing from therefining vessel during at least part of the operation.

2. A process for refining pig iron according to claim 1, wherein therefining vessel is a converter and the height of said foaming slagdivided by the height of the molten metal in the converter is between0.5 and 1.5.

3, A process for refining pig iron according to claim 1, wherein thefoaming slag formed contains fine particles of iron and the slag iscaused to overflow from the refining vessel when it contains 20% or lessof iron.

4. A process for refining pig iron according to claim 1, wherein thefoaming slag overfiowing from the vessel contains particles of iron andcontinuously weighing the slag to determine the percentage of irontherein.

5. A process for refining pig iron according to claim 1, wherein thefoaming slag contains line particles of iron and collecting saidoverflowing foaming slag in a receptacle distinct from the refiningvessel, and separating the slag from the iron entrained with it in saidreceptacle.

6. A process for refining pig iron according to claim 1, wherein thefoaming slag formed contains fine particles of iron in suspension,removing said foaming slag containing fine particles of iron insuspension by continuously overflowing from the refining vessel into areceptacle distinct from said refining Vessel, continuously adding ironinto the refining vessel to make up for the loss of iron from saidrefining vessel, and separating the entrained iron from the entrainingslag, said metal then passing continuously into a secondary refiningvessel in which it is refined again by top blowing while the slag iscollected in a slag ladle.

References Cited UNITED STATES PATENTS 3,145,255 8/1964 Chedaille 75-603,215,424 11/1965 Kanamori 75-60 3,275,432 9/ 1966 Alexandovsky 75-60724,770 4/1903 Young 75-51 1,032,653 7/1912 Brassert 75-52 1,032,6557/1912 Brassert 75-51 2,800,631 7/1957 Suess et al. 75-60 2,962,277 11/1960 Morrill 7560 FOREIGN PATENTS 361,887 11/1906 France.

BENJAMIN HENKIN, Primary Examiner. DAVID L. RECK, Examiner.

Disclaimer 3,356,490.-Francoz's Muller, Griiith, Ind., and Paf/ul Nlles,Embour and Etze'rme Denis, Grivegnee, Belgium. REFININ G PIG IRON. abentdated Dec. 5, 1967. Disclaimer filed June 30, 1969, by the assignee, Instz'tut de Recherches de la Sidemrgz'e Fmvwazse. Hereby enters thisdisclaimer to claims 1, 5 and 6 of said patent.

[Ocal Gazette November .4, 1.969.]

1. IN A PROCESS OF REFINING PIG IRON WHICH COMPRISES TOP BLOWING PIGIRON IN A REFINING VESSEL WITH AN OXIDIZING GAS, THE IMPROVEMENTCOMPRISING PRODUCING A FOAMING SLAG ON THE MOLTEN METAL, AND REMOVING ATLEAST PART OF SAID FOAMING SLAG BY CONTINUOUSLY OVERFLOWING FROM THEREFINING VESSEL DURING AT LEAST PART OF THE OPERATION.